At least you noticed, A lot of people may of missed the fact the fuel was missing and may of flew home the next day. It doesn't even need thinking about what could of happened afterward
You left off a smiley there
I thought you were going to suggest draining out every plane at the local airfield, to see how many pilots never check fuel visually
I bet the results would be pretty scary, especially with some types (twins?).
As said above, video security (over wifi or even over GPRS/3G) is cheap nowadays. I would even put it inside a hangar, to eliminate hangar rash which nobody owns up to.